1. Field of the Invention
The present invention relates to a back light unit, and more particularly, to a back light unit which has common electrodes capable of applying electrical power to light-emitting lamps without soldering.
2. Discussion of the Related Art
Generally, a CRT (Cathode Ray Tube) is employed for a monitor of a TV, of a measuring instrument and of an information terminal. A CRT is not capable of meeting the demands of miniaturization and lightweight due to its own weight and size.
A CRT is expected to be replaced by a LCD (Liquid Crystal Display), a PDP (Plasma Display Panel) and an ELD (Electro Luminescence Device) due to the limit of weight and size. The LCD uses the field optical effect, a PDP uses a discharging gas and an ELD uses the field luminous effect. Studies involving the LCD are presently ongoing.
To replace the CRT, a LCD apparatus is currently under development and has shown to provide many advantages, such as small size, lightweight and low electrical power consumption. Such a LCD apparatus has been applied as a monitor of a lap top computer, a monitor of a desk top computer and a large information display apparatus.
Since a LCD apparatus displays a picture by adjusting the amount of light from the outside, a back light unit is needed as another source of light to irradiate light to a LCD panel.
Generally, a back light unit is classified into an edge type and a direct type according to the disposition of cylinder-shaped luminous lamps.
In the edge type, a lamp unit is installed in the side of a light guide element. The lamp unit includes a lamp emitting light, a lamp holder interposed between both ends of the lamp to protect the lamp, and a lamp reflection sheet for reflecting light emitted from the lamp to the light guide element.
The edge type in which the lamp unit is installed on the side of the light guide element is applied to a small-sized LCD apparatus like a monitor of a lap top computer and a monitor of a desk top computer and has the advantages in producing a flat LCD apparatus with equalized irradiation of light and endurance.
The direct type back light unit has been developed since the size of the LCD apparatus has started to increase to be larger than 20 inches. The direct type back light unit directly irradiates light to the front of the LCD panel by disposing a plurality of lamps on the downstream side of a diffusion sheet.
Such a direct type back light unit is applied to a large screen LCD apparatus demanding high brightness due to a higher light utilization efficiency when compared with an edge type back light.
However, the LCD apparatus employing the direct type back light may cause malfunction of lamps or introduce a short lamp life in the case that a large monitor and a large television employing the direct type back light is operated for a long period. Compared with the edge type unit, there are more possibilities where a LCD apparatus employing the direct type back light may have a lamp not operate due to a malfunction of the lamp and the existence of a short lamp life.
Also, in the case where a lamp does not operate in the edge type, only the brightness of the screen may deteriorate. Since the plurality of the lamps is installed at the down side of the screen in the direct type, the portion in which the lamp does not operate is noticeably darker than the other portions
Thus the lamps must be replaced repeatedly, requiring the LCD apparatus with the direct unit to have a structure of assembly and disassembly without difficulty.
The direct type back light unit according to the conventional systems is described in the following accompanying drawings.
FIG. 1 is a perspective view of a direct type back light unit according to conventional systems. FIG. 2 is a partial view of a direct type back light unit according to the conventional systems. FIG. 3 is a perspective view of a direct type back light unit according to another conventional system. FIG. 4 is a partial view of a direct type back light unit applying electrical power to a lamp according to another conventional system.
As illustrated in FIG. 1, a conventional back light unit comprises a plurality of lamps 1 with electrodes 2 in both ends of the lamps, a lower structure 3 disposed at both ends of the lamps 1 at a predetermined distance and of which the first side forms grooves to accommodate both ends of the plurality of the lamps 1, a reflection sheet 4 mounted on the lower structure 3, a plurality of lamp holders 5 combined in both ends of a pair of the lamps to fix and support the lamps 1 with the lower structure 3, and an upper structure 6 formed along edges of both ends of the lamps 1 to fix the lamp holders 5.
As illustrated in FIG. 2, the lamp 1 is a CCFL (Cold Cathode Fluorescent Lamp) and comprises electrodes 2 provided in both ends inside a lamp tube, an inner lead line 7 for applying electrical power to the electrodes 2, and an out lead line (not shown) connected to the inner line for applying electrical power outside.
The inner lead line 7 and the outer lead line are connected by soldering 9.
The outer lead line is fixed and connected by a contraction tube 11 and a wire 10 connected to an inverter provided in rear of the lower structure 3.
However the conventional back light unit with the above configuration connects by soldering 9 the inner lead line 7 and the outer lead line to apply a driven voltage to the lamps 1. In the process of modulation the soldered portion between the inner lead line and the outer lead line may experience the most stress when a bending force is introduced like, e.g., the interposition of the contraction tube 11, transportation, and the operator's handling.
The above stress may dislodge the soldered portion 9, whereby the inner lead line and the outer lead line becomes disconnected.
The disconnection of the inner lead line and the outer lead line may cause problems such as lighting malfunction, spark generation, and the like.
Consequently, the conventional systems in which the inner lead line 7 and the outer lead line are soldered together has its drawbacks.
As illustrated in FIG. 3 and FIG. 4, another conventional back light unit utilizes a plurality of lamps 31, an outer case 33 fixing and supporting the lamps 31, light scattering means 35a, 35b, 35c disposed between the lamps 31 and a liquid crystal panel (not shown).
The light scattering means 35a, 35b, 35c are employed to prevent appearance of the lamps from becoming visible on a display surface of the liquid crystal panel and to supply a source of light with uniform luminosity distribution. Diffusion sheets and diffusion plates are disposed between the liquid crystal panel and the lamps 31 to enhance the light scattering efficiency.
A reflection sheet 37 is disposed inside of the outer case 33 in order that light generated from the lamps 31 may be irradiated to the LCD panel, resulting in maximizing the light utilization efficiency.
The lamp 31 is CCFL. Electrodes 32 are disposed in both ends of the lamp tube. When electrical power is applied to the electrodes 32, the lamps 31 emit light. Both ends of the lamps 31 are inserted in holes formed on both sides of the outer case 33.
For transmitting electrical power for driving the lamp, leading wires 39, 39a are connected to both electrodes 32 of the lamps 31. Also, the leading wires 39, 39a are connected to a drive circuit through additional connectors, wherein the additional connectors are needed for each lamp.
That is, a leading wire 39 connected to one electrode 32 of each lamp 31 and a leading wire 39a connected to the other electrode 32 of each lamp 31 are connected to one connector and one of the wires 39, 39a bent into a lower part of the outer case 33 is connected to an additional connector.
The wires 39, 39a passing though a hole of an outer case 33 is fixed in an outer case 33 by soldering 40. The outer case 33 may apply an electrical signal to the lamps 31 by soldering 40 as a printed-circuit board.
However, the conventional back light unit has the difficulty of preventing the soldered portion from falling apart, since the wires 39, 39a are fixed in the outer case 33 by soldering 40.